The present invention relates to needles for performing an anesthesia procedure.
The body of a patient has a circumferential tissue layer termed the dura mater surrounding the spinal cord, and a space termed the subarachnoid space between the dura mater and spinal cord filled with cerebrospinal fluid. The dura mater is surrounded by an outer layer of tissue termed the ligamentum flavum.
There are two commonly known types of regional anesthesia procedures, the spinal anesthesia procedure and the epidural anesthesia procedure. In the spinal anesthesia procedure, a thin needle with stylet is pushed through the two layers below the spinal cord into the subarachnoid space, the stylet is removed and proper positioning of the needle is determined by cerebrospinal fluid passing out through the needle hub. Once the needle is in proper position, a suitable drug is injected through the needle which affects the spinal cord nerves and interrupts the ability of the spinal cord to transmit information.
In the epidural anesthesia procedure, a needle containing a stylet is pushed into the body until it contacts the ligamentum flavum which can be felt by an experienced physician. The stylet is then removed from the needle, and a syringe is attached to the needle. The needle is then advanced while pushing on the syringe plunger. When the needle passes through the ligamentum flavum, the plunger falls since there is a loss of resistance when the needle tip is located between the ligamentum flavum and the dura mater, at which time the dura mater is pushed away from the ligamentum flavum creating a space, termed the epidural space. Once the tip of the needle is properly positioned in the epidural space, the syringe is removed from the needle, and an epidural catheter is fed through the needle into the epidural space. The needle is removed from the catheter, and an anesthetic solution can be periodically introduced or injected through the catheter into the epidural space in a continuous manner for an extended length of time.
In the spinal procedure, a small quantity of drug is injected into the subarachnoid space which provides a period of regional pain relief. In order to accomplish the same result in the epidural procedure, it is necessary to inject approximately 10 times the amount of drug used in the spinal procedure. The drug in the epidural space seeps through the dura mater to reach the spinal cord.
A much larger needle is utilized in the epidural procedure than the needle in the spinal procedure. A relatively small needle is required in the spinal procedure, so as to prevent the leakage of cerebrospinal fluid when the needle is removed from the dura mater. If the larger epidural needle is passed through the dura mater, the needle causes such a large opening that the cerebrospinal fluid will subsequently leak through the dura mater which lowers the quantity of cerebrospinal fluid in the cranium which, may result in a severe headache for an extended period of time. Hence, the limited lumen size of the spinal needle makes it difficult to pass a small catheter through the needle into the subarachnoid space.
The difficulty with the spinal procedure is that if the operation is too long, the effect of the drug wears off, and it is not normally possible to perform the procedure again. Hence, another form of anesthesia is then required, such as a general anesthesia in which the patient is placed on a respirator machine which is a difficult complication during the operation.
The main difficulty with the epidural procedure is that it is hard to accomplish without extensive experience by the physician. It is difficult to locate the epidural space, and the physician may accidently puncture the dura mater during the epidural procedure.
Some attempts have been made to place a catheter into the subarachnoid space to perform a continuous spinal anesthesia procedure. Some of these attempts are disclosed in the following publications:
Continuous Caudal Analgesia to Produce Painless Childbirth, J. Indian M. A., Vol. 63, No. 1, July 1, 1974, pp. 38, Continuous Procaine Spinal Anesthesia for Cesarian Section, Anesthesia and Analgesia, Vol. 51, No. 1, Jan.-Feb., 1972, pp. 117, Methemoglobinemia and Infant Response to Lidocaine and Prilocaine in Continuous Caudal Anesthesia: a Double--Blind Study, Anesthesia and Analgesia, Vol. 48, No. 5, Sept.-Oct., 1969, pp. 824, Experiences with Continuous Spinal Anesthesia in Physical Status Group IV Patients, Anesthesia and Analgesia, Vol. 47, No. 1, Jan.-Feb., 1968, pp. 18, Continuous Spinal Anesthesia with Hypobaric Tetracaine for Hip Surgery in Lateral Decubitus, Anesthesia and Analgesia, Vol. 51, No. 5, Sept.-Oct., 1972, pp. 766, Spinal Subdural Hematoma Associated with Attempted Epidural Anesthesia and Subsequent Continuous Spinal Anesthesia, Anesthesia and Analgesia, Vol. 59, No. 1, Jan. 1980, pp. 72, Continuous Caudal Analgesia in Obstetrics, Proc. Roy. Soc. Med. Vol. 26, Feb. 1969, pp. 185, Continuous Caudal Epidural and Subarachnoid Anesthesia in Mares; a Comparative Study, Am. J. Vet. Res., Vol. 44, No. 12, pp. 2290, The Strange Case of the (Inadvertent) Continuous Spinal, John Sherratt & Sons Ltd., pp. 82, The Position of Plastic Tubing in Continuous--Block Techniques, an X-ray Study of 552 Patients, Anesthesiology, Sept.-Oct., 1968, pp. 1047, Esperienze Cliniche Sulla Anesthesia Spinale Continua, Acta Anesthesiologica, 1968, pp. 49 and Raquianestesia Continua Em Pacientes de Idadea Idadea Avancada, Rivista Brasilcira de Anestesiologia, Ano 20, N. 4, Out-Dez.--1970, pp. 518.
However, in such procedures there is difficulty with the size of the needle and catheter. The relatively thin needle is relatively weak, and may bend. Also, it is difficult to thread the relatively small catheter through the needle.